1. Field of the Invention
The present invention relates to, for example, an optical unit including a variable magnification optical system and to an image capturing apparatus including this optical unit.
2. Description of the Prior Art
In recent years, digital cameras have been increasingly widespread which employ an image sensor, such as a CCD (charge coupled device) or the like, that converts an optical image into an electrical signal. As is the case with cameras employing a silver halide film, there has been a demand for such digital cameras to be miniaturized (downsized) and simplified in structure.
Many of optical systems capable of magnification variation (variable magnification optical systems) for use in a digital camera or the like have lens units provided with a positive, a negative, a positive, and a positive optical powers (refractive powers). In such a variable magnification optical system, in order to achieve a simplified structure, the first lens unit closest to the object side is not moved during magnification variation (zooming) or the like in some cases.
However, as is the case with a conventional variable magnification optical system (zoom lens), the immovability of the first lens unit is likely to result in an increase in the full length and the lens diameter (for example, front lens diameter) of the zoom lens. To control such a tendency, there is a magnification variation method of moving the first lens unit. However, although reducing the full length and the lens diameter of the zoom lens, this method leads to a complicated structure.
Thus, this conventional zoom lens adopts a method of not moving the first lens unit while moving the fourth lens unit closest to the image side to thereby achieve downsizing of the lens diameter and the like.
However, with only the magnification variation method of not moving the first lens unit while moving the fourth lens unit, there is a limit to the downsizing of the lens diameter and the like.